There is currently work ongoing within the Third Generation Partnership Program (3GPP) to introduce a new Radio Access Technology (RAT). The new RAT is called E-UTRAN (Evolved Universal Mobile Telecommunications System Terrestrial Radio Access Network), and is also known as Long Term Evolution (LTE). One item to be specified is the interworking between E-UTRAN and the other existing RATs, such as Global System for Mobile Communication/Enhanced Data rates for GSM Evolution (GSM/EDGE) Radio Access Network (GERAN) and Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN).
In order to inform mobile stations in a cellular radio system about neighboring E-UTRAN cells, the procedure is to broadcast information about the neighboring (allowed) E-UTRAN frequencies and an optional “black list” of not allowed neighboring E-UTRAN cells for each of the E-UTRAN frequencies. The E-UTRAN cells are then identified through their Physical Layer Cell Identities (PCID), which is an identity that is locally unique per E-UTRAN frequency. Efficient coding of sets of PCIDs is currently being discussed within 3GPP for the case where a group of PCIDs needs to be blacklisted, e.g. at country borders. The reason is that the information about what E-UTRAN cells that are blacklisted or which are not blacklisted needs to be sent on the broadcast channels. The broadcast channels typically have a very limited capacity and hence there is a need to limit the use of the resources of the broadcast channels as far as possible.
In comparison, the information about neighboring GERAN and UTRAN cells is sent as lists of allowed neighboring GERAN and UTRAN cells. Cells are divided into different areas, within GERAN and UTRAN into Location Areas/Routing Areas and within E-UTRAN into Tracking Areas. Each cell thus belongs to a Location Area/Routing Area (GERAN and UTRAN) or a Tracking Area (E-UTRAN).
When a mobile station (in GERAN mode) performs measurements for cells that belong to non-GERAN access technologies, such as UTRAN and E-UTRAN (LTE) the mobile station is unaware of the Location Area/Routing Area/Tracking Area they belong to. Also in some scenarios a mobile station is not allowed to enter a specific Location/Routing/Tracking Area. This becomes apparent when the mobile station tries to perform cell reselection to a cell in that area. For the GERAN to UTRAN case today the mobile station is then not allowed to try cell reselection to any UTRAN cell on the same frequency for a certain time, a back off time. The reason is that the mobile station is not aware of what Location/Routing Areas the other UTRAN cells belong to.
Thus, when the mobile station is in an area with different Location/Routing/Tracking Areas, where some are allowed and some are not, the mobile station will in some scenarios not be able to perform cell reselection to any of the allowed cells due to that cell reselection was attempted for a not allowed cell/area the first time. This can be either in idle mode or in packet transfer mode where the mobile station controls the cell reselection/handover (in NC0 and NC1 modes).
In case the mobile station is in dedicated mode or packet transfer mode, the mobile station would in the corresponding scenarios be performing unnecessary measurements, and transmit unnecessary measurement reports, of cells that belong to not allowed Location/Routing/Tracking Areas. The list of not allowed areas is kept in the mobile station based on previous rejected accesses in those areas.
Hence, there exist a need for a method and a mobile station that eliminates or reduces the problems encountered when performing cell reselection.